Ok, I have chicks in 3 age groups. 6 weekers, 4 weekers and, 2 weekers. Are any of them old enough to give dewormer to?

They are too young to worm unless you have seen worms in their droppings. I would wait until they are 3 months old, and either take in several of their droppings to your vet to be checked for what worms they may or may not have, or start them on a twice a year regimen. Valbazen is a very good one to use with a dosage of 1/4 ml for a chick, 1/2 ml for a regular 5 lb chicken, and 3/4 ml for a large chicken or rooster given orally, then repeat this dose after 10 days to get the worm eggs. The cleaner and drier their coop and run are, the less worms they may have. All chickens can have worms, and wormers help to keep them from having an overload. If you live in a hot wet environment, some people worm 4 times a year. Always follow a 14 day egg withdrawal time after the last dose of wormer.